1. Field of the Invention
The present invention pertains to lifting clamps for use in lifting and conveying metal plate and other structural elements and more specifically the present invention pertains to a tooth wear indicator and method for use with lifting clamps.
2. Background
Lifting clamps typically have an eccentric cam with a curved surface. The curved surface includes a number of rounded serrations or teeth. These rounded serrations or teeth hold the element being lifted by biting into a surface. The holding force exerted by the lifting clamp is increased in direct proportion to the lifting or conveying effort exerted. The greater the lifting force, the greater the holding force and consequently, the greater the wear on the cam teeth.
Lifting clamps designed for lifting and conveying heavy metal plates, various metal structural shapes and other elements such as material storage drums are subject to rough handling and rapid wear. Such rapid wear is caused by the stressful nature of their use. These lifting clamps are typically used in harsh environments where abrasive or corrosive materials are often caught between the cam teeth and the element being lifted. These corrosive or abrasive materials contribute to the rapid wear of the gripping teeth on the cam portion of the lifting clamp.
Since lifting clamps are normally found in applications employing relatively unskilled laborers, it is preferable that a convenient and easy to use wear indicator be provided for the rounded serrations or teeth on the cam surface. Such a wear indicator should provide a quickly read measure of tooth wear for the clamp user so that worn cams in lifting clamps can be replaced before a dangerous condition occurs.
When tooth wear approaches a point which would diminish the cam tooth penetration or the bite into the element being lifted, the lifting capability of the clamp is reduced to a potentially dangerous level. Such a dangerous situation is particularly critical if a worn clamp is used with an abnormally heavy load. Accordingly, an effective wear indicating system may substantially reduce the risk of serious injury or death.
A problem associated with most wear indicating systems relates to the relative difficulty associated with inspecting the teeth once the cam is mounted in the lifting clamp. Typically, the type of clamp with which the present invention is used includes a somewhat inverted "U" shaped jaw. The cam is supported within the inverted "U" shaped jaw for pivotal movement, which movement is used to urge the cam into gripping engagement with the plate or structural member being lifted. The cam in the lifting clamp is usually disposed in the recess formed by the "U" shaped jaw and hence is not easily accessible for visual inspection or measurement with special wear gauges. The problem of effective cam tooth wear measurement is aggravated by the low light conditions often found in material storage areas in warehouses or factories. Accordingly, there is a need to provide a convenient wear indicating system which can be read in low light conditions or by touch. Such wear indicating system should reveal the condition of the rounded serrations or teeth between lifting operations. Finally, such measurement system should not require that the lifting clamp be disassembled or that any special measuring tools be used.